The present invention relates to a platinum compound and a process of preparing the same.
Heretofore, compounds (I) and (II) have been known as platinum compounds having carcinostatic effects. The compound (I) has been obtained by means of the following procedures. At first, the compound (II) is prepared by reacting K.sub.2 Pl(II)X.sub.4 (X is Cl or Br) with a 1,2-cyclohexanediamine isomer. A silver nitrate solution of two equivalents in respect to the compound (II) is added to a solution prepared by dissolving the compound (II) into water under boiling to precipitate chlorine or bromine as silver chloride or silver bromide which is then filtered off. To the filtrate is added an organic dibasic acid to obtain the desired compound (I). ##STR1##
However, this preparation process possesses a disadvantage that many impurities such as the unreacted compound (II), compounds (III) and (IV) which are by-products of the compound (II) and an unreacted silver ion remain in the compound (I) prepared according to the above process.
One of the reasons the impurities are contaminated in the desired compound (I) is the low solubility of the compound (II) in water. For example, when the compound (II) is a chloride of a trans-1 isomer, its considerably low solubility in water is about 0.26 mg/ml and oven if dissolved under boiling, only about 0.5 mg/ml of the compound (II) dissolves. Because of the low solubility of the compound (II), it is quite difficult to completely dechlorinate the compound (II) from the viewpoint of its characteristics resulting in the contamination of the above impurities.
A remarkable problem also remains in the removal of the silver chloride formed as a result of the above reaction. The solubility of the silver chloride is relatively low so that almost all the silver chloride formed can be removed in ordinary conditions. However, in the above reaction, a large amount of water is required due to the low solubility of the compound (II) so that the complete removal of the silver chloride may be impossible in such a reaction employing a large amount of water.
This tendency becomes worse when the bromide is employed.
Many platinum compounds may possess physiologic activities such as cytotoxicity, and the contamination of the above unreacted compound (II) and the by-products (III) and (IV) is not allowed in the raw material for medicines having carcinostatic effects even if a trace amount. The unreacted silver ion which may exist in the medicines is regulated in a heavy metal test method, but no satisfactory value in connection with the silver ion has been obtained in conventional methods.